1. Field of the Invention
The present invention relates to a stage-drive controlling device used in a scanning projection exposure apparatus for transferring the pattern of a mask to a. photosensitive substrate via a projection optical system while synchronously scanning a mask stage for holding the mask and a substrate stage for holding the photosensitive substrate in a predetermined scanning direction. More particularly, the present invention concerns a stage-drive controlling device having a characteristic in controlling the speed of the mask stage and the substrate stage.
2. Description of the Related Art
Conventionally, a scanning projection exposure apparatus is known as a kind of exposure apparatus which is used in the manufacture of semiconductor devices, liquid-crystal display devices, and the like through a photolithographic process. In brief, this scanning projection exposure apparatus transfers the pattern of a mask (or reticle) to a photosensitive substrate via a projection optical system while synchronously scanning a mask stage for holding the mask and a substrate stage for holding the photosensitive substrate in a predetermined scanning direction.
The scanning projection exposure apparatus synchronously scans the mask stage and the substrate stage at a speed ratio (4:1) which is determined by the projection magnification of the projection optical system. This synchronous scanning controls the stages by imparting respective targeted values to the speed controlling systems of the respective stages. In this case, a signal representing a difference between the position of the substrate stage and the position of the mask stage is supplied to the speed controlling system of the mask stage. Fox this reason, the signal representing the difference changes when the substrate stage begins to be moved by the speed controlling system on the substrate stage in such a manner as to follow the speed command signal, and the changed signal is supplied to the mask-side speed controlling system so as to accelerate the mask stage in a direction which the difference indicates. The mask-side speed controlling system is a type of controlling system which is generally comprised of a PID controller and the like having an integrating function. The acceleration is effected until the positions of the two stages are aligned, and the mask and the photosensitive substrate are finally scanned synchronously.
However, with the system in which the scanning speed of the mask stage is increased or decreased by detecting the difference between the substrate stage and the mask stage while the substrate stage is moved, there is a drawback in that the time from the acceleration of the mask and the photosensitive substrate until the synchronous scanning becomes long. In particular, as the demand for a larger-size mask (reticle) grows large, the time until the synchronous scanning has become increasingly longer.
Accordingly, from the viewpoint of reducing the time until the synchronous scanning, a stage-drive controlling device has been proposed in which the mask stage is comprised of a relatively large coarsely moving stage and a compact and lightweight finely moving stage which moves relatively over the coarsely moving stage along the scanning direction, as disclosed in U.S. Pat. 5,477,304 corresponding to Japanese Patent Application Laid-Open No. 140,305/1994. In this stage-drive controlling device, the speeds of the coarsely moving stage and the substrate stage are controlled by their respective speed controlling systems at a predetermined speed ratio, and an attempt is made to control the position of the finely moving stage in synchronism with the speed control based on the speed controlling systems of the coarsely moving stage and the substrate stage such that the substrate stage and the finely moving stage assume a predetermined positional relationship.
However, since the speeds of the substrate stage and the coarsely moving stage are controlled independently of each Other, strictly speaking, a positional error unfailingly occurs between the two stages. If a disturbance is not present in the two stages, this positional error becomes a fixed value during scanning, so that it suffices if the finely moving stage is capable of coping with a targeted value which does not fluctuate over time during scanning.
FIG. 6 shows an example of the positional error between the coarsely moving stage and the substrate stage during scanning. If the speeds of the Coarsely moving stage and the substrate stage completely coincide with each other from a scanning start, the positional error becomes zero.
In actuality, however, some speed error occurs. In a case where the speed error is present only during acceleration, the positional error waveform becomes such as the one indicated by the chain line A in FIG. 6. The position controlling system of the finely moving stage is the so-called one-type control system which is generally provided with one integrator and an open-loop transfer function has one pole in the origin. If the positional difference between the coarsely moving stage and the substrate stage is a fixed value such as the one indicated by the chain line A, the position controlling system of the finely moving stage is capable of completely absorbing this positional error. However, in a case where when the positional error between the coarsely moving stage and the substrate stage changes in the form of lumps as indicated by the double-dashed line B in FIG. 6, or the positional error changes over time in the form of lumps as indicated by the solid line C and a disturbance of sinusoidal waves, such as the rocking of the body is superposed thereon, the positional controlling system of the finely moving stage which is the one-type control system cannot completely absorb the positional error, and a residual error occurs.
Accordingly, in order to realize high-resolution scanning exposure by using the finely moving stage, it is indispensable to ensure that the lump-like or sinusoidal positional error does not occur between the mask-side coarsely moving stage and the substrate stage, or is minimized as practically as possible.